The present invention relates to a method of manufacturing a semiconductor device, particularly a high voltage transistor with high reliability.
It is known to use a stabilizing resistor in series with an emitter for a semiconductor device of a meshed emitter structure or multi-emitter structure, and that the emitter is made of a plurality of portions for the purpose of obtaining a high output. It is advantageous to use a polysilicon film as the stabilizing resistor for the emitter.
It is also known to provide a high-resistance sheet over a pn junction surface to enable the pn junction to block a high reverse voltage, so that the form of a depletion layer region related to the pn junction is changed to reduce the electric field strength in the depletion layer region, and to attain a high blocking voltage with high reliability. It is also advantageous to use a polysilicon film as the high-resistance sheet.
Thus, polysilicon films can be used as both the stabilizing resistor for the emitter and the high-resistance sheet over the pn junction surface. However, the resistance of the stabilizing resistor and that of the high-resistance sheet are about 10 .OMEGA./.quadrature. and 10.sup.10 .OMEGA./58 , respectively, the difference between which is very large. For that reason, there is a drawback that a single polysilicon film cannot be used as both the stabilizing resistor and the high-resistance sheet.